In this paper the dependence of build-up233U,232U,233Pa and fission products from ThO2 irradiated in HFETR on integral thermal neutron fluxes and neutron spectra have been investigated. The yields of all above nuclides in ThO2 increase with the increase of integral thermal neutron fluxes at different neutron spectra. The values of233U/232Th increase with the increases of th and decreases with the increase of fast/thermal neutron ratios (f/th). The values of232U/233U increase with the increase of both th and f/th ratio. The amount of fission products relative to original irradiated thorium decreases with the increase of f/th ratios. These results could be used to evaluate the behaviour of thorium-based nuclear fuel in reactor.